xf86drmMode: smoke-test the atomic API

As going through the modetest patches for atomic support I've noticed
that if we pass NULL for the drmModeAtomicReqPtr argument we'll crash.

So let's handle things appropriately if the user forgot to check the
return value of drmModeAtomicAlloc and drmModeAtomicDuplicate or made a
typo somewhere along the way.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rob Clark <robclark@freedesktop.org>
Cc: Daniel Stone <daniels@collabora.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

xf86drmMode.c

@@ -1189,6 +1189,9 @@ drmModeAtomicReqPtr drmModeAtomicDuplicate(drmModeAtomicReqPtr old)
 {
 	drmModeAtomicReqPtr new;
 
+	if (!old)
+		return NULL;
+
 	new = drmMalloc(sizeof *new);
 	if (!new)
 		return NULL;
@@ -1213,6 +1216,9 @@ drmModeAtomicReqPtr drmModeAtomicDuplicate(drmModeAtomicReqPtr old)
 
 int drmModeAtomicMerge(drmModeAtomicReqPtr base, drmModeAtomicReqPtr augment)
 {
+	if (!base)
+		return -EINVAL;
+
 	if (!augment || augment->cursor == 0)
 		return 0;
 
@@ -1239,11 +1245,14 @@ int drmModeAtomicMerge(drmModeAtomicReqPtr base, drmModeAtomicReqPtr augment)
 
 int drmModeAtomicGetCursor(drmModeAtomicReqPtr req)
 {
+	if (!req)
+		return -EINVAL;
 	return req->cursor;
 }
 
 void drmModeAtomicSetCursor(drmModeAtomicReqPtr req, int cursor)
 {
+	if (req)
 		req->cursor = cursor;
 }
 
@@ -1252,6 +1261,9 @@ int drmModeAtomicAddProperty(drmModeAtomicReqPtr req,
 			     uint32_t property_id,
 			     uint64_t value)
 {
+	if (!req)
+		return -EINVAL;
+
 	if (req->cursor >= req->size_items) {
 		drmModeAtomicReqItemPtr new;
 
@@ -1309,6 +1321,9 @@ int drmModeAtomicCommit(int fd, drmModeAtomicReqPtr req, uint32_t flags,
 	int obj_idx = -1;
 	int ret = -1;
 
+	if (!req)
+		return -EINVAL;
+
 	if (req->cursor == 0)
 		return 0;